1. Field of the Invention
Embodiments of the invention generally relate to methods and compositions for forming conformal coatings on substrates having a textured surface. More specifically, embodiments of the invention generally relate to sol-gel processes and sol-gel compositions for forming low refractive index conformal coatings on textured transparent substrates.
2. Description of the Related Art
Glass that it is highly transmissive to visible light is often highly desirable for many applications including semiconductor device manufacturing, solar cell manufacturing, glass manufacturing, and energy cell manufacturing. One method for increasing the transmission of glass is to pattern or texture the surface of the glass substrate. The transmission of light through the patterned or textured glass may further be enhanced through the use of coatings that provide low reflectivity or a high percent transmission over a broad wavelength range of light.
A conformal coating deposited on a textured glass substrate, meaning that the thickness of the coating conforms to the surface patterns of the textured glass substrate, will achieve greater transmittance than a textured substrate with a non-conformal coating deposited thereon. However, if there is some variation in the conformality of the coating, then maximum transmittance will not be achieved. Therefore in order to achieve maximum transmittance, it is desirable to form conformal coatings on textured glass substrate.
One method of depositing coatings on substrates is through the use of sol-gels. Sol-gel processes are those where a wet formulation (the “sol”) is dried to form a gel coating having both liquid and solid characteristics. The sol is mostly liquid based with the components of the sol evenly distributed in the sol system. The gel coating is then treated to form a solid material. The gel coating or the solid material may be formed by applying a thermal treatment to the sol.
However, if after application of the sol to the textured substrate, the sol remains in a low viscosity liquid phase for an extended period of time, the low viscosity sol will flow from the field portions of the textured substrate into the wells of the textured substrate leading to a thicker coating in the wells of the substrate relative to the fields of the substrate which forms a non-conformal coating upon drying. This non-conformal coating is undesirable as it may lead to a decrease in transmittance.
Thus there is a need for coatings and methods for coating textured glass which results in a conformal coating across the textured glass and thus increases the transmission of visible light through glass.